U.S. Senator Bernie Sanders is gaining on Democratic front-runner Hillary Clinton, but experts say Clinton is still likely to grab her party's nomination to run for president in 2016.

While the senator from the U.S. state of Vermont has long been in Washington, he has never grabbed the major media headlines he is getting now.

Sanders, a self-proclaimed "Democratic socialist," is drawing large crowds with his speeches on income inequality at a time when many Americans are still struggling financially.

At the same time, the Clinton campaign in recent months has seen a firestorm of controversy over her use of a private email account as secretary of state, and she has been under investigation by the Federal Bureau of Investigation over whether she compromised national security.

The controversy is dogging her campaign, but even worse for her is that heavy hitters in her own party have blasted her for how she has handled the scandal.

In a recent Des Moines Register/Bloomberg Politics poll of likely Iowa primary voters, Sanders is now just seven points behind Clinton, almost doubling his portion of the vote since May.

Republican strategist Ford O'Connell told Xinhua that Clinton is likely aware of Sanders' surge because she is moving toward the left on a number of issues.

Sanders is moving up fast because of Clinton's inability to put the email fiasco behind her, coupled with her seeming reluctance to admit that Sanders is catching up and an unwillingness to address it.

"That said, I don't think it's going to be Bernie Sanders who takes down Hillary Clinton," O'Connell said, adding that Clinton is still the most hopeful to win the nomination.

"The real question for Clinton is how long can she continue to ignore him?" he said.